Fibrillation process

ABSTRACT

A method of fibrillating ribbon or tape, by subjecting the material to at least two fluid false-twisting means such that the direction of twist imparted to the material is completely reversed between adjacent false-twisting means. The material may be polyamide, polyester or mixture of these two and it may be heated prior to passing into the false-twist means and relaxed after passing therethrough.

United States Patent [191 Ostrowski et al.

1*Nov. 13, 1973 FIBRILLATION PROCESS [75] Inventors: Henry S. Ostrowski,Charlotte,

N.C.; John F. Roberts; John G. Blacker, both of I-Iarrogate, England[73] Assignee: Imperial Chemical Industries Limited, London, England 1Notice: The portion of the term of this patent subsequent to Mar 13,1988,

has been disclaimed.

[22] Filed: Aug. 13, 1969 [21] Appl. No.: 849,672

[30] Foreign Application Priority Data Aug. 19,1968 (ireatBritain39488/68 [52] US. Cl. 57/167, 28/D1G. 1, 57/34 B, 57/157 F [51] Int. ClD02g 3/06, D02g 1/16 [58] Field of Search 57/34, 34 B, 77.3-77.45,57/140, 157, 157 F, 167; 28/DIG. 1, 1 F, 72 CS [56] References CitedUNITED STATES PATENTS 3,382,663 5/1968 Frielingsdorf 57/167 X 3,702,05511/1972 Kosaka et al 57/157 F X 2,515,299 7/1950 Foster et a1... 57/157UX 3,177,557 4/1965 White 57/157 X 3,186,155 6/1965 Breen et al. 57/1403,293,844 12/1966 Wininger et al.. 57/157 3,395,525 8/1968 Eddy 57/167 X3,470,594 10/1969 Kim 28/1 F UX 3,494,522 2/1970 Kim et a1. 28/1 F X3,500,626v 3/1970 Sandiford 28/72 X FOREIGN PATENTS OR APPLICATIONS864,695 4/1961 Great Britain 57/34 B Primary ExaminerDonald E. WatkinsAttorney-Leonard Horn and Stephen D. Murphy [57] ABSTRACT A method offibrillating ribbon or tape, by subjecting the material to at least twofluid false-twisting means such that the direction of twist imparted tothe material is completely reversed between adjacent false twistingmeans. The material may be polyamide, polyester or mixture of these twoand it may be heated prior to passing into the false-twist means andrelaxed after passing therethrough.

7 Claims, 4 Drawing Figures FIBRILLATION PROCESS The present inventionconcerns improvements in or relating to filamentary materials and theirproduction and particularly to yarns, threads, cords or otherfilamentary articles which are made by fibrillation techniques.

It is known to produce filamentary articles from longitudinally orientedfibrillatable synthetic polymeric tapes or films by subjecting them tobeating or twisting actions to cause them to fibrillate. One such knownmethod of fibrillating involves subjecting a fibrillatable tape or filmstrip to the beating action of fluid flowing in a highly turbulentstream at high velocity whilst the material is kept slack or under verylow tension but this method suffers from the disadvantage that controlof fibrillation is poor because of the difficulty of maintaining the lowtension at a relatively uniform level. This poor control overfibrillation leads to variable products, which also have more freefibril ends and fibril loops than is desirable for many end uses. Otherknown methods of fibrillation involve brushing or slitting fibrillatablestrands, which severe mechanical actions, give products having many freefibril ends and loops and also reduce the physical properties of thestrand. Acoustic and electrostatic means, optionally associated with amechanical action, have been proposed but such methods necessitatecostly apparatus. Still other known methods involve twisting thefibrillatable film strip, for instance by means of a ring-spinningmachine or a mechanical false twister, so that it undergoes asubstantial reduction in its transverse dimension and, in the case ofthe false twisting process, is then subjected to a sudden change indirection. Such methods necessitate slow processing speeds to producesufficient fibrillation for many purposes.

It is an object of the present invention to provide a method forfibrillating a fibrillatable ribbon or tape which does not suffer fromthe disadvantages of the aforesaid prior art methods.

According to the present invention, there is provided a method forfibrillating a fibrillatable ribbon or tape which comprises subjecting atravelling fibrillatable ribbon or tape under tension to the action of aseries of at least two fluid false-twisting means such that thedirection of twist imparted to the strand is completely reversed betweenadjacent false-twisting means. Preferably there is substantially nochange in longitudinal direetion of movement of the strand between thefirst and second false-twisting means.

We believe that the complete reversal of twist in the material betweenadjacent false-twisting means imposes intense stressing and shearingforces which causes very effective fibrillation.

The term ribbon as used herein means an elongated structure wider thanit is thick which is produced by extrusion ofa melt of a thermoplasticpolymer or a solution thereof through a slot or a number of slots in aspinneret or die and the term tape is used herein to denote an elongatedstructure of ribbon form but which is produced by extruding or castingthe thermoplastic polymer into a film which is longitudinally slitbefore or after orientation into a number of narrower widths. As is wellknown a high degree of longitudinal orientation, preferably uniaxialorientation is necessary to produce a fibrillatable tape or ribbon.

We have found that insertion of false-twist into the ribbon or tape bymeans of contra-rotating fluid streams gives more effective fibrillationof a ribbon or tape than insertion by mechanical false twisting means,due to an undefined secondary action of the fluid which augments thefibrillation caused by the complete reversal of twist in the strand andproduces enhanced uniformity of fibrillation. In addition the spacing ofconsecutive fluid jets has little effect upon the fibrillation produced.

The fibrillatable ribbons or tapes used in the present invention may bemade from any polymeric substance capable of producing such ribbons ortapes and particularly useful substances are polypropylene, polyarnides,polyesters and melt blends of incompatible polymers. Tapes and films ofenhanced fibrillation tendency comprising a plurality of spaced parallelstriations longitudinally aligned with the axis of orientation andthinner webs integral with and extending between the striations are alsosuitable for use in the present invention. Likewise fibrillatable,conjugate ribbons or tapes which comprise two or more superposed layersof film adhered together which films may have different shrinkagepropensities may be used in a method according to this invention. Incertain cases fibrillation may be affected by heating the fibrillatableribbon or tape. One particular effect of heating a ribbon or tape, thatis before passing it through contrarotating fluid jets and allowingtwist to run back into the heating means, is described hereinafter. inanother case, wherein heating precedes fluid jet treatment and twist isnot allowed to run back into the heating means, fibrillation of lesseasily fibrillatable ribbons may be enhanced. Finally, heating ofaribbon or tape may be effected between stages of false twisting, whichhas the effect of somewhat reducing the fibrillation. In general,however, heating between stages is not desirable. The dimensions of theribbons or tapes used may vary depending upon the apparatus used and theproduct desired and can be chosen accordingly. Thus for thicker ribbonsor tapes a higher fluid pressure and/or a lower speed of movement of aribbon or tape through the fluid twisting means would be used. Also tofurther enhance the fibrillating effect twist stopping guides may bepositioned upstream and downstream of the fluid twisting means toconfine the false twist effects within a shorter length. Alternativelytreatment in a series of two or more pairs of contrarotating fluid jetsmay be used, preferably arranged to produce alternating directions oftwist throughout the whole series of fluid jets.

Air is the preferred fluid for use in a process according to thisinvention but other fluids, as for example steam, which do not have adeleterious effect on a ribbon or tape being treated, may be used.

Ribbons or tapes treated according to the present invention may be useddirectly, for example in the production of cords or textile articles ora certain amount of true twist may be inserted before such use of thefibrillated materials. The usefulness of the treated materials may beenhanced by carrying out a treatment according to the invention in amanner which imparts a tendency to contract to a bulky, elasticstructure.

Thus according to a further aspect of the invention we provide a processas hereinbefore described wherein the twist imparted by the first fluidfalsetwisting means is allowed to run back over a hotplate or into aheating zone positioned before the falsetwisting means. Carrying out theprocess in this way allows at least a part of the first inserted twistto be heat set into the ribbon or tape, this set twist being temporarilyremoved, reversed and removed again in the following false-twistingdevices. A ribbon or tape treated in this way when allowed to relaxpartly or completely will tend to return to the set twisted conditionand in doing so will develop bulk and elasticity. The bulk so developedmay be set in and the elastic properties modified by a further heattreatment under controlled tension or partial relaxation conditions atan elevated temperature, usually higher than the first heat settingtemperature. Heat treatments as described may be applied in continuousmanner by suitably positioned heating and relaxing means or the secondheat treatment may be applied to a package of fibrillated material whichhas been wound up at a lower speed than the speed or delivery from thelast false-twisting device, i.e., which has been overfed to the windingunit, such over-feeding providing the necessary tension relaxation.

As stated hereinbefore the method of the present in vention producesvery good fibrillation of enhanced uniformity, and this is shown by thelow fibril deniers and ratios of fibril width to fibril thicknessesobtained in the fibrillatable products. Also fewer free fibril ends andfibril loops may be obtained and the product of the ratio of fibrilwidth to fibril thickness and free fibril ends per cm. for the productsproduced by the method of this invention may be considerably lower thanin the prior art products because of the inherently better controlpossible in the present invention. Free fibril ends in this contextinclude all ends and loops which protrude from the product at least 1mm.

The invention will now be described in more detail by way of Example andwith reference to the accompanying drawings, of which FIG. 1 shows anarrangement of apparatus for fibrillating fibrillatable structuresaccording to the invention, FIG. 2 shows a device for producing twocontra-rotating fluid vortices and FIGS. 2a and 2b are cross-sectionsthrough the device of FIG. 2.

Detailed construction of a device which applies reversing false twist bymeans of contra-rotating fluid vortices is shown in FIGS. 2, 2a and 2bwherein the device 11 is a U-shaped member through the parallel limbs22, 22' of which are coaxial bores 23, 23' the axes of which borescoincide.

Bores 23, 23' are provided with radially aligned parallel-sided slots25, 25 which facilitate the stringing-up of the device. Manifold bore 29is provided in the interior of the device, and is axially parallel withcoaxial bores 23, 23'. Manifold bore 29 is connected to a pressurizedfluid supply (not shown) by means of connector 31. From manifold bore 29fluid passageways 27, 27' pass and enter bores 23, 23' tangentially andperpendicularly to the axes of said bores 23, 23'. The exit orificesfrom passageways 27, 27' are positioned in the walls of bores 23, 23' soas to produce fluid vortices rotating in opposite directions in limbs22,22.

In operation, pressurised fluid enters manifold bore 29 and passestherefrom by way of fluid passageways 27, 27' into coaxial bores 23, 23'whereby fluid vortices which are contra-rotating with respect to eachother are generated in bores 23, 23'. A travelling fibrillatable ribbonor tape passes through coaxial bores 23, 23' and is false-twisted ineach bore by action of the contra-rotating fluid vortices. The directionof the false-twist imparted to the ribbon or tape is reversed at a pointsubstantially mid-way between parallel limbs 22, 22' whereat intensetraverse shearing forces and stresses are induced in the ribbon or tapecausing it to fibrillate and to form many fine fibrils. In the followingExamples the diameters of passages 25 and 25' and 27 and 27 arerespectively 4.8 and L6 mm.

We have found that more regular products are obtained when thetwist-reversal point in the strand is maintained substantiallystationary in spaced and the apparatus of FIG. 2 is particularly usefulin this connection.

EXAMPLE I As shown in FIG. 1, an undrawn tape 1, consisting of a meltblend of polymers of composition 95.5 percent polyhexamethyleneadipamide and 4.5 percent polypropylene, having a denier of 4,860, awidth of 9.5 mm and a thickness of 0.055 mm is drawn and fibrillated bythe following route. The tape 1 is first drawn between two rollers, 3and 5, with associated idler rollers 4 and 6 arranged so that the tapefollows a helical path on the roller assemblies having differentperipheral speeds in the ratio of l 5, to produce drawn, oriented tape 7having a denier of 975, a width of 5.0 mm and a thickness of 0.028 mm.The drawn tape 7 is immediately and continuously fed at a speed of 18metres per minute to a heating zone 9 and it is then passed at a tensionof 49 grams through two contra-rotating air vortices produced by the jetdevice 11 shown in detail in FIG. 2, operating at a line-pressure of10.2 kg/cm gauge. Pigtail guides 13 and 15 are placed before and afterthe fibrillating device 11 in a position which allows the jet device llto generate a swirling balloon in the tape, having 6 nodes, with a node17 positioned halfway between the contra-rotating fluid vorticesgenerated by the device ll. After fibrillation the fibrillated tape iswound up on a constant tension winder 19.

The fibrillated tape has the following properties:

Denier of product 1035 Mean denier of fibrils l2 Fibril width tothickness ratio (W)/(T) 2.4 Fibril free ends/cm 1.5 (W)/(T) free ends3.6 Tenacity (grams per denier) l.6

The fibrillated tape is a compact bundle of substantially rectangular(the narrow ends of some fibril crosssections being somewhat rounded)cross-section fibrils having little longitudinal variation in the numberof fibrils and showing few free ends or loops.

EXAMPLE 2 An undrawn tape of the same size as used in Example 1 butconsisting wholly of polyhexamethylene adipamide is drawn in the sameway to produce tape of 1,034 denier which is fibrillated as in theforegoing Example to produce a product having the following properties:

Denier I059 Mean fibril denier l4 W/T ratio 2.7 Free fibril ends/cm. 4.0W/T X free ends l0.8 Tenacity (g./den.) 0.8

EXAMPLE 3 Apparatus according to FIG. 1 slightly modified is used todraw, fibrillate and impart bulk to a tape of polyethylene terephthalate(intrinsic viscosity measured in o-chlorphenol at 25 C. of 0.67)measuring 6 mm wide and 0.044 mm thick in the undrawn condition. TheFIG. 1 apparatus is modified by providing means to heat feed roll 3 to asurface temperature of 100 C., a hotplate cm long and of surfacetemperature 200 **C. between rolls 3 and 5 and dispensing with the guide13 which allows the twist to run back through the heating zone 9 whichis also a hotplate 20 cm long of surface temperature 220 C.

The tape is drawn between rolls 3 and 5 to draw ratio of 5.8:1 at a drawspeed of 61 metres per minute giving a drawn tape 2.5 mm wide and 0.013mm thick. The device producing two contra-rotating fluid vortices issupplied with air at a line pressure of 5.6 kg per square centimetre andthe fibrillated tape is wound up at a tension of 40 g and a speed of 61metres per minute.

The bulky fibrillated product had a denier of 600 (compared with adenier of 400 for the drawn unfibrillated tape) a number of free fibrilends and a network structure when unravelled with the means fibrildenier being 10.

EXAMPLE 4 EXAMPLE 5 A tape of polyethylene terephthalate as used inExample 3 is drawn as in that Example using an electrically heated ovenoperating at 180 C in place of the hotplate 9 to give a drawn tapemeasuring 2.4 X 0.009 mm (270 denier) which is fibrillated as in Example3 and heat treated at 200 C in the relaxed state producing a bulkymaterial of 348 denier and 4.0 mean fibril denier.

EXAMP LES 6-9 In these Examples a series of four air jets is used tofibrillate a polyethylene terephthalate tape as used in Example 4, eachjet causing a twist counterto that of the immediately preceding jet, allbeing supplied with compressed air at a pressure of 5.6 Kg/cm. With thisarrangement for the same overall consumption of air, 0.23 cubic metresper minute, as used for two jets amarkedly improved fibrillation isproduced as the following table, wherein processing speed is varied,shows Speed Mean fibril denier Example (m./min.)

Four jets Two jets The use of four jets enables either a higher speed oran economy of air consumption to be used or a finer fibrillation to beobtained. In fact fibrillation is almost independent of processing speedwith a plurality ofjets.

EXAMPLES 10-13 In these Examples two contra-rotating air jets are usedto fibrillate a polyethylene terephthalate tape as used in Example 4 andthe distance between the two jets is varied. This as shown in thefollowing Table has only a small effect on the extent of fibrillationproduced:

Distance between Mean fibril jets (cm.) denier the spacing used inExamples 19.

COMPARATIVE EXAMPLES A AND B cation No. 797,051 are used. In both caseseach device is operated so as to reverse the direction of twist appliedto the tape in its passage therethrough and are spaced 3.5 cm. apart;other processing conditions and the mean fibril denier of the productsare given in the following Table:

From the Table it can be seen that the mechanical false twisting meansare both slow and inefficient fibrillation means.

EXAMPLE 14 A conjugate tape 5 mm. wide and 0.032 mm. thick is preparedby casting a thin film of polyethylene terephthalate (intrinsicviscosity 0.65) on top of a thin simultaneously cast film of a polyestercomprising moles percent ethylene terephthalate and 20 moles percent ofethylene isophth alate and longitudinally slitting into 5 mm. tapes. Acast conjugate tape is then drawn to a draw ratio of 6.96:1 as inExample 3 (feed roll surface temperature 80 C.) giving a drawn tape of275 denier measuring 1.9 X 0.012 mm. which is fibrillated as in thatExample. The fibrillated product on heat relaxation at 80 C developsincreased bulk. The relaxed material has a total denier of 503 and amean fibril denier of 8.8.

EXAMPLE 15 An isotactic polypropylene tape is produced with longitudinalparallel striations interspersed with thinner integral webs by meltextrusion through a shaped die and is oriented by drawing to a drawratio of 7:1. The drawn tape of 1,830 denier and 6.5 mm width isfibrillated in a device producing two contra-rotating air vorticesoperated at an air pressure of 4.6 Kg. per sq.cm., the yarn speed being150 m. per minute and the winding tension 183 g. A coarse, open networkproduct results having an average fibril denier of 53.

What we claim is:

1. A method for fibrillating a fibrillatable ribbon or tape whichcomprises subjecting a travelling fibrillatable ribbon or tape undertension to the action of a series of at least two fluid false-twistingmeans such that the direction of twist imparted to the strand iscompletely reversed between adjacent false-twisting means.

2. A method according to claim 1 wherein there is substantially nochange in longitudinal direction of movement of the strand between thefirst and second or succeeding false-twisting means.

3. A method according to claim 1 wherein the twist imparted by the firstfalse-twisting means is allowed to run back over or into a hotplate orheating zone positioned before the false-twisting means.

4. A method according to claim 3 wherein the material after passagethrough the false-twisting means is allowed to relax at least partially.

5. A method according to claim 1 wherein the ribbon or tape is heated inthe absence of twist before passing into a fluid false-twisting means.

6. A method according to claim 1 wherein the fluid is air.

7. A method according to claim 1 wherein a ribbon or tape is composed ofpolypropylene, a polyamide, a

polyester or mixtures of any of these polymers.

2. A method according to claim 1 wherein there is substantially nochange in longitudinal direction of movement of the strand between thefirst and second or succeeding false-twisting means.
 3. A methodaccording to claim 1 wherein the twist imparted by the firstfalse-twisting means is allowed to run back over or into a hotplate orheating zone positioned before the false-twisting means.
 4. A methodaccording to claim 3 wherein the material after passage through thefalse-twisting means is allowed to relax at least partially.
 5. A methodaccording to claim 1 wherein the ribbon or tape is heated in the absenceof twist before passing into a fluid false-twisting means.
 6. A methodaccording to claim 1 wherein the fluid is air.
 7. A method according toclaim 1 wherein a ribbon or tape is composed of polypropylene, apolyamide, a polyester or mixtures of any of these polymers.